BOZEMAN, Mont. -

Lenny Brown has always been a gun owner.

"I've owned firearms all my life" he said. "I've been an NRA member all my life."

He is also a medical marijuana card holder. But now, the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) say he can't legally be both.

"Federal law here says that if you are an unlawful user or addict, you are a prohibited person" said ATF Public Information Officer out of Denver, Bradley Beyersdorf.

The federal government considers all users of medical marijuana unlawful, no matter what state law says.

The ATF outlined its position today in a letter to federal firearms licensees. In short, it tells them that they cannot sell any firearms or ammunitions to cardholders.

"If somebody who is planning to purchase a firearm and identifies themselves as a medical marijuana card holder" he says, then the gun retailer "should not sell that firearm to that individual."

The ATF tracks the sales of all firearms from Federal Firearms Licensees (FFL) in the United States.

Beyersdorf said that if "somebody goes to purchase a firearm from an FFL, they have to fill out ATF form 4473."

Form 4473 includes several yes or no questions. One asks if the applicant is a "user of" or "addicted" to unlawful substances including marijuana.

Beyersdorf said card holders have to answer yes, which means their application will be denied.

"I was pretty devastated" said Brown, when he saw the ATF's letter. "I felt like my 2nd Amendment rights have been dissolved."

Brown said he thinks the denial comes down to a rights issue, and hopes to see legal action.

NBC Montana called several gun dealers in Bozeman, but they had not seen the letter yet and had no comment.

You can read the ATF's letter by clicking here.